Solid-state imaging devices are used for, for example, cameras for cellular phones, digital still cameras (DSCs), and high definition (HD) movie cameras, as a device to obtain the image information of an object.
Moreover, in a solid-state imaging device, unit pixels having photodiodes are arranged in an array on a silicon semiconductor substrate. Moreover, a microlens provided above a photodiode collects light from an object and the photodiode receives the collected light. Moreover, a signal read circuit outputs signal charges generated by photoelectric conversion at the photodiode. Through a series of these operations, the solid-state imaging device can obtain image information.
When such a solid-state imaging device captures color images, a color filter is provided between the photodiode of each pixel and a microlens. This color filter transmits only the light of a desired wavelength range among incident light from an object. The solid-state imaging device receives light of the desired wavelength range at the photodiode, and performs arithmetic processing, based on an obtained signal output, thereby obtaining a color image. A fine particle pigment filter is generally used for this color filter. Moreover, for good color separation, this color filter requires a film thickness of around 1 μm.
On the other hand, pixels have been microfabricated in recent years in order to achieve smaller solid-state imaging devices and higher resolution of captured images. For instance, solid-state imaging devices having minute pixels of around 1.0 μm have been developed. Following the microfabrication of this pixel size, the light receiving area of a photodiode in a unit pixel, i.e., an aperture ratio has been decreasing. This makes it difficult to maintain high sensitivity at a minute pixel. This also leads to increase in the distance between a microlens and a photodiode, the width of a photodiode, and an aspect ratio. Thus, light collected at the microlens not only enters a photodiode in the same pixel, but also enters a photodiodes in an adjacent pixel. In other words, optical color mixing occurs.
To solve such problems, backside illumination solid-state imaging devices have been in development in which light enters a surface opposite to a surface where a signal read circuit is formed.
Moreover, general backside illumination solid-state imaging devices need to collect electric charges generated in a light receiving part on a side opposite to the side of an illumination surface, i.e., a surface where a signal read circuit is formed.
In the related art shown in Patent Literature 1 discloses a technique by which a transparent electrode is provided on the illumination surface side of the light receiving part in a backside illumination solid-state imaging device, and a potential gradient is generated in the light receiving part by bias to the transparent electrode. Thus, the solid-state imaging device recited in Patent Literature 1 can easily collect electric charges. Indium thin oxide (ITO) is used, for example, in this transparent electrode.